but as to using ss1 as a high-speed suborbital transport vehicle i think they need both height and length (i.e. increased efficiency or more power)

For a transport you need not only altitude but also range. SS1 can get altitude -- that's exactly what it's designed for. SS1 can not get range -- that's exactly what it's not designed for. It is extremely impractical to use a true rocket engine for a suborbital transport -- you don't really need to exit the atmosphere except for the coast phase (if at all) -- which is why NASA and the DOD have been playing around with hypersonics for a while. With the X-43A, they've proven it's possible. From here on, their job is to make hypersonic aero/spaceplanes that are big enough to carry a payload. Then we just need to figure out a way to make it economical.

i think there is an opportunity for using a modified ss1 for suborbital hops as mentioned in the first post of this topic (but only by going suborbital, that's why i put the stress on height and lenght)

airbreathers are great but it will be some time until they're ready for "consumption"

I disagree that airbreathers (IE Scramjets) are usefull for orbital vehicles. They have, at this time, one use only: supercruise missiles. It was annoying that NASA was stuck with the X-43 program when it should have come out of DOD budget, because ultimtately it will be the USAF and Navy that reaps the benefits of scramjets.

IMO 2 things are relevant:

1: Suborbital is a means to an end. The space tourism economy will begin here, but hopefull it will lead to cheaper access to orbit. When that is achieved, the suborbital market will go back to being the near void that it was (er.. is) While it will be nice to take a 15 minute joyride in the future, I think we all know, that's not really what we want when we think about going to space. We wan't Bigelow to build a hotel and a cheaper way to get there.

2: Hypersonic airbreathing engines are mostly dead weight on any spacecraft save for boost-glide suborbitals. Orbital LV's do not spend very long in the atmosphere at all, so they have little to gain in benefit from using an airbreathing first stage. Case in point: there is only one orbital LV at this point with an airbreathing first stage, the Pegasus XL. The Pegasus is, dollars to payload, one of the most expensive launchers in the world. While I doubt anyone expects to see a SSTO with scramjets on it anymore, at the same time, the added complexity with little to gain by using an airbreathing first stage (regardless of whether it uses turbines, scramjets, or Roton's whirlygig thingy.)

On the boost-glide issue, IIRC Len Cormier had done some design work on a vehicle that would have done just that, as a rapid fright delivery system. Wakeboarding the atmospher. I love it.

i agree, but i see a future for airbreathers as a more efficient wk-style first stage (not much dead weight in a first stage) for any orbital second stages (not only sub-orbital). they might have a competing edge in economics of scale as they would be usable for both boost stages as well as in hypersonic flight (which would probably be their "big" market) while (what i think will be) their main competition would be single stage rockets/shuttles using aerospike technology (only in the sub-orbital/orbital market).

would love to get some feedback giving a comparison between sub-orbital intercontinental flight versus hypersonic (possibly airbreathing) intercontinental flight. what are the pros and cons of the different methods? which would be fastest when travelling west (against the earths rotation)?